We just learned an old debt (over 7 years old) just took all our money from our checking account! What can we do? Can they do this? Nobody notified us...

If they had your correct address on file you should have been notified. They can only take money from your accoutn if they sue you in court. Have you received collection letters from them in the past few years or anything saying they would sue?

Is the creditor the Federal government?
The cleaned out my checking acount without notice a few years ago.
I hadn't filled a quarterly GST form(GST is a Canadian sales tax) for a business account so they estimated the amount owing.
I agree with Lowtax4eva the bank will not give out money from your account with proper authority.
How did they get the money out?
I would check with the bank and see if fraud was involved. The creditor may have posed as you to get the money out.
Is it possible you signed a pre-authourized withdrawal aggrement with the Creditor and they just tracked you down?
I had a tenant that gave me a bad check. I went to the bank on a regular basis to see if they had money in the account. It was six months later,long after they had been evicted before I could cash the check so I bet they didn't even realize the check was still valid.